Recently, the amount of digital data, which are shared by a lot of people, has been tremendously increased, while digital devices such as digital cameras, camera-attached mobile communication instruments, digital camcorders and MP3 players are popularized. Since digital data are being frequently produced and widely shared, digital data should be systematically managed. However, it may be difficult to manage digital data (e.g., search and information extraction) due to the massive amount of the information therein.
A scheme for classifying or integrating digital data by using a tag is widely known as one of the conventional techniques for managing digital data. A “tag” can be understood as additional data attached to digital data for the purpose of accessing or searching for the digital data as quickly as possible. Such a tag is generally comprised of a series of characters, numbers, or a combination of numbers and characters.
There are various types of tags as follows: a space tag, a person tag, an object tag, a time tag and the like. Especially, a lot of attempts have been made to extract the person tags from digital data with a high accuracy.
FIG. 7 describes a face recognition by using a face appearance feature and a contextual feature. In this regard, Microsoft Research Asia has published an article entitled “Automated Annotation of Human Faces in Family Albums” in 2003. This article discloses a technique of adding the contextual feature to the conventional face recognition algorithm in order to improve a recognition rate of people included in images of photos. The contextual feature represents that people included in images of a plurality of photos taken on the same day or in the same event may wear the same clothes. Such contextual feature can be used to distinguish each of the people in the photos.
According to the above-mentioned article, the face recognition algorithm based on the contextual feature cannot be applied to two or more sheets of photos taken on distant dates, e.g., at intervals of three or more days. Thus, the article says that the photos are required to be taken within at most two days to apply such similarity, i.e., the contextual feature.